The purpose of this research program is to identify and classify on a formal basis the characteristics which are essential to proper functioning of a knee joint. The second goal is to test in the laboratory a variety of endoprostheses to attempt to predict causes of failure. Insofar as possible, laboratory data will be correlated with clinical data obtained through gait studies in this center and other centers, initially to validate the laboratory testing methods. The ultimate objective is to establish a protocol for pre-clinical testing of knee prostheses. At the present time, several types of endoprostheses are being widely used clinically and characteristic modes of failure are gradually being identified. A large number of other types of prostheses including patellar replacements have been used with less frequency and with less well identified failure characteristics. Through the results of the research program, it is hoped that a large proportion of the mechanical failures encountered in total knee replacement procedures in humans can be avoided by a thorough pre-clinical biomechanical testing system.